[$] Toward safer GNU C Library tunable handling

When considering the interface provided by the GNU C Library (glibc),thoughts naturally turn to the programming interface as specified by POSIX,along with numerous extensions added over the years. But glibc alsoprovides a "tunables" interface to control how the library operates; ratherthan being managed by a C API, tunables are set with theGLIBC_TUNABLES environmentvariable. Glibc tunables have been a part of a few security problemsinvolving setuid binaries, most recently the "LooneyTunables" bug disclosed at the beginning of October. The glibcdevelopers are now considering significant changes to tunable handling inthe hope of avoiding such problems in the future.